A wide variety of thermal printers are known to those of ordinary skill in the art. Such thermal printers render images by transferring donor materials in an image wise fashion from a donor web to a receiver medium. Typically, such donor materials are arranged on the donor web in patches of differently colored donor material and a color image is formed on the receiver medium by applying donor material from each of the differently colored donor patches onto the same portion of the receiver medium. Often, a donor web will also provide a patch containing a protective material that is clear and that protects the image from environmental degradation. The protective material must also be applied to the same portion of the receiver medium that bears the image formed by the donor materials. Accordingly, it will be appreciated that color and even monochrome image formation using such printers requires precise alignment of the donor receiver medium relative to a printhead that is used to transfer the donor material to the receiver medium so that donor material from each of the patches and the laminate patch are applied in perfect registration on the receiver medium.
Thus what is needed in thermal printing is a medium transport system that is capable of providing a receiver medium at a particular location relative to a printhead in a fashion that can be repeatedly reproduced at least a minimum number of times for an individual image to be rendered by the printer.
There are a variety of solutions to this problem. In some thermal printers, the recirculation is provided by mounting the receiver medium on a drum such as a vacuum drum from which holds the medium in a precise alignment so that the receiver medium can be moved past a printhead in a repeatable number of cycles. Alternatively, drums are also known that hold a receiver medium using electrostatic forces and/or mechanical clamps. However, the use of such drums increases the size, weight, and cost of the thermal printer.
Other printers such as the highly popular Kodak Easyshare Printer Dock have been developed that use pinch-rollers positioned near a thermal printhead to grip the receiver medium so as to provide control over the movement of the receiver medium such that reciprocal presentation of the receiver medium to the printhead with precise registration is possible. However, such pinch roller type arrangements increase the cost, size, and complexity of the printer and further, in many applications, the use of pinch roller type arrangements requires the use of receiver medium that is oversized longitudinally with respect image recorded thereon. This leaves unprinted marginal areas in an image generated by such printers. These unprinted marginal areas must be removed to provide a satisfactory experience. It will be appreciated that this wastes receiver medium and increases the cost of prints generated by such printer.
Thus what is needed in the art is a new method and apparatus for transporting a receiver medium past a thermal or other imaging head multiple times in a manner that allows donor materials to be applied in a registered manner to the receiver medium from each color patch and/or from a laminate patch in complete registration but without requiring the use of the medium retaining drums, or pinch rollers, or any other medium transport that otherwise requires the use of an oversized medium relative to the image formed thereon.